Interesting discussion coming up on twitter.
Everybody paying attention already knows Blood DKs have scary strong runic power generation due to Blood spec's powerful synergy between Haste and Multistrike from the Runic Strikes passive (listed as Blood Rites below) and the Veteran of the Third War passive. We all looked at that in beta, decided it was clearly going to be a problem in later gear tiers, and provided consistent feedback saying so.
It was not fixed, and so far is not fixed for 6.1. Hope we can change that here today.
Back in beta we figured it would lead to an interesting choice between bleeding off extra Runic Power to Conversion or Breath of Sindragosa in later raid tiers. But we missed a few points. First is that the glyph of Icy Runes offers a ton of Runic Power generation. But who cares, right? That eats Frost runes, which means you can't Death Strike, which means you're a much less useful tank, so that's a potentially interesting (and possibly OK) tradeoff.
Thing is, until now, nobody actually tested it in a raid. When you're:
1) Generating 1 RP/sec passively from VotTW passive
2) Generating 15 RP whenever an autoattack multistrikes from Runic Strike/Blood Rites passives. (And autoattack speed scales with haste, remember. That's the dangerous synergy between those two stats.)
3) Get +10% Haste and multistrike from the VotTW passive
4) Get an additional 5% Multistrike from the Runic Strikes passive
5) Glyph Icy Runes so Chains of Ice generates 20RP from each Frost rune, and spend most Frost and Death runes on Chains of Ice
6) Gear for multistrike, and get a bunch of it as gear improves throughout the expansion
Well, you can keep Breath of Sindragosa up forever, performing like Simetrik and substantially outdamaging DPS DKs. You're a crappy tank, true. But you can replace a DPS so who cares?
Now I fully expect the devs to simply nerf the glyph of Icy Runes. But that's the wrong way to go, it will just delay the problem until we get enough Haste and Multistrike from later gear and are back in the same spot. The right way is to fix Runic Strikes/Blood Rites to eliminate the synergy between Haste and Multistrike. DKs should be constrained by their resources. The real problem is Blood's resource generation. If that isn't fixed, it will cause problems elsewhere.